Descemet stripping automated endothelial keratoplasty is being performed in increasing number of cases each year. An adequate scleral rim on all sides is mandatory for the donor cornea to be mounted on the artificial anterior chamber for microkeratome-assisted dissection. Occasionally, the scleral rim may however be inadequate. The primary cause of inadequate scleral rim is poorly trained technicians in in-situ excision technique. Hence, we devised a novel technique for performing successful microkeratome-assisted dissection in donor corneas with inadequate scleral rim. A surrogate scleral rim was obtained from the donor tissue not fit for optical keratoplasty. It was then glued to the optical grade donor cornea that had an inadequate scleral rim either focally or circumferentially. The combination was then used for a successful microkeratome-assisted dissection followed by endothelial keratoplasty.
- Eye (Tissue) Banking
Statistics from Altmetric.com
Descemet's stripping automated endothelial keratoplasty (DSAEK) is a partial thickness corneal transplant procedure to replace primarily the endothelium of the cornea. Automated microkeratome dissection is preferred over manual dissection as it is associated with lower incidence of perforation and faster visual recovery.1 An adequate scleral rim2 (>3.6 mm) on all sides is mandatory for corneal scleral tissue to be mounted on the artificial anterior chamber (AAC) for microkeratome-assisted dissection. A tighter seal decreases the chances of tissue collapse during the movement of microkeratome.3 Due to unavailability of enough well-trained technicians in a developing country setup who are familiar with in-situ excision technique, there is a high probability of obtaining inadequate scleral rim (<3.6 mm) in donor tissues. This along with the paucity of good-quality donor tissues has created an imminent shortage of donor corneas that can be used for DSAEK procedure.
Continuous rise in proportion4 ,5 of cases suitable for DSAEK as compared with penetrating keratoplasty led to a looming need to use the donor corneas with insufficient rim (<3.6 mm) for DSAEK procedure. Hence, in order to expand the pool of donor tissues for DSAEK surgery, we devised this novel technique. A surrogate scleral rim, obtained from the donor tissue not fit for optical keratoplasty, was tailored and glued to the optical grade donor cornea that had an inadequate scleral rim either focally or circumferentially.
The eligibility criteria for surrogate donor corneosclera included a minimum diameter of 15 mm and a minimum limbal-scleral edge distance of 5 mm. The eligible surrogate donor corneosclera with poor optical quality was retrieved from MK medium (Aurora, Buffalo, New York, USA) and placed on a Teflon block with endothelial side up. A full thickness 11.5 mm trephination was done from the endothelial side. It was ensured that the entire cornea along with the scleral rim, which measures about 0.5 mm, was encompassed in the area of trephination (figure 1). In case the trephination was not complete, Castroviejo corneoscleral scissors were used to complete the separation.
Hence, a surrogate scleral rim with at least 3.5 mm breadth was obtained on all the sides. The rim was then dried using a merocel sponge. The surgical technique is shown in detail in online supplementary video 1.
The donor cornea suitable for optical keratoplasty, but with an inadequate scleral rim, was retrieved from Optisol medium (Bausch & Lomb, St Louis, Missouri, USA) and then placed (with endothelial side down) on the AAC (Moria, Antony, France). Precautions were taken to avoid any air bubble underneath. AAC system was flushed with balanced salt solution (BSS) while carefully centreing cornea on top of the piston. Infusion was continued with BSS and cornea slightly moved to remove any air bubbles underneath.6 Once the air bubbles were completely removed, the infusion was stopped. The scleral rim was dried with merocel sponge, and both the components of Tisseel VH Fibrin sealant (Baxter AG, Vienna, Austria) were applied over it (figure 2). The dried surrogate scleral skirt was placed over the rim and gentle pressure was applied to achieve optimal adhesion for 1 min (figure 3). The anterior chamber cover was then placed on the base-locking ring so that the tabs of the cover fit into the open spaces on the base. The cover was locked into the base by turning it 15° clockwise. The piston was then raised up and tightened completely. After ensuring a high intraocular pressure (IOP) of at least 65 mm Hg, the tube was clamped at a distance of 30 cm from AAC. Ultrasonic probe was placed on the central surface to check the corneal pachymetry. The microkeratome head was then mounted on the guide ring and was followed by a smooth excursion to separate the anterior lenticule of the cornea. Turbine pedal was then released and the microkeratome lifted off. Subsequently the vacuum pedal was turned off.
The diameter of the cut was assessed and a central ultrasonic pachymetry was repeated. Posterior central lamellar thickness of the cut was assessed. Intraoperative optical coherence tomography (OCT; OPMI LUMERA 700) was used to assess the uniformity of the cut. The keratectomy edges were stained with Gentian violet to help in subsequent centration during trephination of the donor tissue. The anterior cap was placed back and the lamellar grafts carefully dismounted without collapsing the chamber. The lamellar grafts were then placed endothelial side up on the standard punch trephine block. It was then punched with the help of an appropriately sized trephine.
This technique was performed by two surgeons (NS and TA) in 20 donor corneas with inadequate scleral rim. High IOP could be generated in all the cases without any difficulty. The mean (±SD) preoperative central pachymetry of donor corneas was 554.2 µm (±23.2). All cases were performed with the 400 µm microkeratome head. The mean (±SD) postoperative ultrasonic central pachymetry of donor corneas was 128.2 µm (±12.1). The mean diameter (±SD) of the cut was 8.11±0.26 mm. All the donor posterior lamellas were well centred and uniform on an intraoperative OCT assessment in terms of peripheral thickness of the lenticule. No perforation was encountered in any of the donor eye. The mean (±SD) percentage endothelial cell loss during the procedure was 2.5% (±1.9%).
DSAEK remains the most preferred type of posterior lamellar keratoplasty in recent times.5 ,7 It allows a selective replacement of diseased host endothelium with a suitable and healthy donor posterior lamella. The major advantage of the posterior lamellar or endothelial keratoplasty procedure in comparison with PK is that the normal corneal surface of the recipient is retained because of the avoidance of surface corneal incisions and sutures.8–11
Endothelial keratoplasty is now the most common keratoplasty procedure performed in the USA.5 However, the donor selection prerequisites like preoperative donor cell count ≥2300 cells/mm2 and adequate scleral rim (>3.6 mm) on all the sides poses restrictions over the number of eyes that can be used for DSAEK especially in the developing countries where this procedure is evolving.12
Studies comparing the two different procurement techniques of in-situ excision versus whole globe enucleation in a large, single eye bank series found no difference in terms of endothelial cell density.13 ,14 With in situ excision technique, highly skilled eye bank technicians are required to achieve an adequate (>3.6 mm) scleral rim on all the sides. However, due to dearth of highly skilled eye bank technicians, we often receive corneas with an inadequate scleral rim (<3.6 mm) that are not amenable to DSAEK. Taking feedback and communicating with the eye-bank technicians that harvest the corneas is of paramount importance. Lack of expertise in Descemet membrane endothelial keratoplasty (DMEK) at our centre precludes these corneas with inadequate corneal scleral rim to be used for it. In future, however, with increase in trained eye bank technicians and growing expertise of surgeons in DMEK procedure, this new surgical technique may have limited indications.
Nahum et al15 hypothesised the technique of using 360° scleral skirt for microkeratome dissection of corneosclera with inadequate scleral rim but were unsuccessful due to lack of air tightness. Adjunctive use of fibrin glue in our series may have led to successful outcomes. However, the major limitation with this technique was the increased financial burden due to utilisation of fibrin glue while the major drawback was the extra time spent in fashioning the surrogate scleral rim. Cyanoacrylate glue although a more economical option was not considered as it polymerises very rapidly compared with fibrin glue. Hence, it would not give enough time to adjust the surrogate scleral skirt to ensure an adequate rim on all sides. Also, the polymerisation of fibrin glue is more uniform than cyanoacrylate and hence would not cause any uneven elevation of the scleral skirt.
The mean diameter of the cut was 8.11 mm and was therefore optimal to achieve an 8 mm regular posterior lamellar grafts required in most of our cases. Size of the cut and requirement for donor graft size may however vary depending on geographic population and white-to-white diameter of the donors.
Presently, this technique is a simple way of providing a surrogate scleral rim to the corneas with endothelial cell count ≥2300 cells/mm2 but an inadequate scleral rim. It is a simple, reproducible and efficient way of utilisation of eye bank tissues and will be vital in handling the increasing proportion of DSAEK surgeries being performed each year.
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
- Data supplement 1 - Online video
Contributors NS, TA and TA: contributions to the conception or design of the work or the acquisition, analysis or interpretation of data. TA and MK: Drafting the work or revising it critically for important intellectual content. NS, JST and TA: Final approval of the version published. JST and MK: Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.